1. Field of the Invention
The present invention relates to a communications network and a method of operating a communications network.
2. Description of the Related Art
Recently, the demand for streaming video to a computer via the Internet has grown strongly. This has led to a need to supply increasing amounts of video material over local communication networks (including the copper pairs used by telephone network operators or the coaxial cables used by cable television network operators).
In telephony networks this additional demand is being met partly by the introduction of Digital Subscriber Loop (DSL) technology. As its name suggests, this technology carries digital signals over the local copper loop between a user's home and a local telephone exchange. Data-rates of several megabits per second to the user's home have become commonplace. Advances in this technology now lead to much higher rates, 20 Mbit/s and above and with plans in the industry to offer 50 Mbit/s and above to a substantial proportion of broadband end users in the relatively near future. Using DSL, the digital signal is conveyed between modems placed at either end of the copper loop. The advantages of statistical multiplexing have led to the digital signals being organised into transport packets (whether they be Asynchronous Transfer Mode (ATM) packets or Ethernet packets. Over either of these are carried Internet Protocol (IP) packets conveying all of the broadband services.
Cable networks have also been upgraded to carry broadband services to user's homes. Substantial numbers of users currently receive broadband services over cable and, again, the services are conveyed using IP packets over Ethernet.
Video material requires a data rate which varies between 1.5 Mbps (for a quality comparable to that offered by a video cassette recording) to 20 Mbps (High-Definition Television). In DSL or cable networks, these higher application data rates means that a mechanism is needed to manage contention for the capacity available towards the user's home. This capacity management includes both the maximum available capacity for any one user and the shared capacity towards the DSL Access Multiplexer (DSLAM) or Cable Modem Termination System (CMTS). This capacity (sometimes termed “backhaul” capacity) may be shared by several hundred users, and contention for the capacity will also need to be managed as users demand more choice in the material they view.